To corrugate the surface of a conventional pile sheet, for example, an apparatus such as shown in FIG. 8 is used. In this apparatus, a rotary roll 101, a spiral cutter 102 and a lower blade 103 are disposed as shown. When a spiral sheet 104 is conveyed in between the rotary roll 101 and spiral cutter 102, the front end of piles 105 is cut off by the spiral cutter 102 and lower blade 103.
The rotary roll 101 is undulated by integrally forming coils 106 on the surface, for example, as shown in FIG. 9. Thus, corresponding to the coils 106 are cut shorter than other piles 105, so that the surface of the pile sheet 104 is undulated.
When the pattern is formed by cutting the piles 105, removing the waste cuttings of cut piles 105 is indispensable. This takes time in processing. Besides, the waste cuttings of the pile 105 are very tiny and light, floating in the air, and, hence, the working environment is contaminated.
Moreover, the spiral cutter 102 and lower blade 103 must be sharpened after a number of uses. Thus, work must be interrupted, and the processing takes a very long time.